Trapezoid Area Calculator

About this calculator

A trapezoid has exactly one pair of parallel sides, called the bases. Its area is found by averaging the two base lengths and multiplying by the perpendicular height between them: Area = ((a + b) / 2) × h. This works because a trapezoid can be split into a rectangle and triangles, or equivalently thought of as the average of a shape that’s “all short base” and one that’s “all long base,” both at the same height.

The formula is a staple of land surveying, where irregular plots are often approximated as a series of trapezoids to compute total area (the basis of the trapezoidal rule in surveying), and of civil engineering, where the cross-section of canals, drainage channels, and highway embankments is frequently trapezoidal by design. Roof framers and carpenters use the same formula for trapezoidal roof sections and stair stringers.

Enter the two parallel side lengths and the height, and this calculator applies the trapezoid area formula directly.